Shift Fork Boss Oil Hole Layout for Thin Dog-Clutch Transmissions
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Solution Overview
Problem
Existing dog-clutch type stepped transmissions face challenges in efficiently supplying oil to the slidable portions of shift forks, leading to insufficient oil supply and increased complexity due to the need for narrow oil paths, which complicates machining and hinders the reduction of shift fork thickness.
Innovation Solution
The design incorporates a shift fork with a cylindrical boss portion and a base plate portion where the oil hole is formed in the boss portion, allowing for a larger oil hole without increasing the base plate thickness, and a depressed portion guides oil to the slidable area, enabling direct and efficient oil supply without requiring a narrow hole inside the base plate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a narrow oil path is formed inside the shift fork to supply oil directly to the slidable portion, then oil supply efficiency is improved, but machining difficulty increases and shift fork thickness cannot be reduced
Solution Approach 1:
The patent moves the oil hole formation from the base plate (two-dimensional surface) to the boss portion (three-dimensional cylindrical structure). This dimensional change allows the oil hole to be drilled radially through the boss portion, providing direct access to the slidable portion without requiring narrow passages through the base plate thickness.
Solution Approach 2:
The shift fork is divided into functionally distinct portions: the boss portion (for oil supply and structural support), the base plate portion (for shifting function), and the slidable portion (for engagement). This segmentation allows each portion to be optimized independently - the boss portion handles oil supply while the base plate thickness can be reduced for size reduction.
2Volume of moving object
If the shift fork thickness is reduced to minimize transmission size, then overall transmission size is reduced, but forming an oil path inside the shift fork becomes difficult
Solution Approach 1:
The oil supply path is relocated from the base plate thickness direction to the radial direction of the boss portion. This allows the oil hole to be formed by radial drilling through the boss portion, independent of the base plate thickness, enabling thin shift forks while maintaining oil supply capability.
Solution Approach 2:
The boss portion acts as an intermediary structure that mediates between the oil supply requirement and the thin base plate design. The oil hole through the boss portion serves as the intermediary pathway, delivering oil to the slidable portion without requiring thick base plates or complex internal passages.
3Device complexity
If oil is supplied indirectly to the slidable portion of the shift fork, then the structure is simpler, but oil supply amount becomes insufficient
Solution Approach 1:
The oil supply function is extracted from the base plate structure and concentrated in the boss portion. The oil hole through the boss portion provides a dedicated, high-volume oil supply path directly to the slidable portion, separating the lubrication function from the shifting structure.
Solution Approach 2:
The oil is supplied to the slidable portion before the shifting operation occurs. The oil hole is positioned to deliver oil directly to the contact surface between the slidable portion and the gear, ensuring lubrication is available in advance of any friction or wear events.
Data Source
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AI summary
A shift fork 90 includes a boss portion 91 through which a shift fork shaft 100 is inserted, a base plate portion 92, a first arm portion 93, a second arm portion 94, and a slidable portion 95 that slides on a slide ring 50. The boss portion 91 includes a oil hole 97 that communicates with a oil supply path 103 inside the shift fork shaft. A depressed portion 160 is formed in the base plate portion 92, wherein the depressed portion 160 is located outward in the radial direction of the boss portion 91. The depressed portion 160 extends from the oil hole 97 toward the slidable portion 95.